Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers

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Le 28/01/2020 à 04:33, Qian Cai a écrit :

On Jan 27, 2020, at 10:06 PM, Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote:

On 01/28/2020 07:41 AM, Qian Cai wrote:

On Jan 27, 2020, at 8:28 PM, Anshuman Khandual <Anshuman.Khandual@xxxxxxx> wrote:

This adds tests which will validate architecture page table helpers and
other accessors in their compliance with expected generic MM semantics.
This will help various architectures in validating changes to existing
page table helpers or addition of new ones.

This test covers basic page table entry transformations including but not
limited to old, young, dirty, clean, write, write protect etc at various
level along with populating intermediate entries with next page table page
and validating them.

Test page table pages are allocated from system memory with required size
and alignments. The mapped pfns at page table levels are derived from a
real pfn representing a valid kernel text symbol. This test gets called
right after page_alloc_init_late().

This gets build and run when CONFIG_DEBUG_VM_PGTABLE is selected along with
CONFIG_VM_DEBUG. Architectures willing to subscribe this test also need to
select CONFIG_ARCH_HAS_DEBUG_VM_PGTABLE which for now is limited to x86 and
arm64. Going forward, other architectures too can enable this after fixing
build or runtime problems (if any) with their page table helpers.

Hello Qian,

What’s the value of this block of new code? It only supports x86 and arm64
which are supposed to be good now.

We have been over the usefulness of this code many times before as the patch is
already in it's V12. Currently it is enabled on arm64, x86 (except PAE), arc and
ppc32. There are build time or runtime problems with other archs which prevent

I am not sure if I care too much about arc and ppc32 which are pretty much legacy

enablement of this test (for the moment) but then the goal is to integrate all
of them going forward. The test not only validates platform's adherence to the
expected semantics from generic MM but also helps in keeping it that way during
code changes in future as well.

Another option maybe to get some decent arches on board first before merging this
thing, so it have more changes to catch regressions for developers who might run this.

ppc32 an indecent / legacy platform ? Are you kidying ?

Powerquicc II PRO for instance is fully supported by the manufacturer and widely used in many small networking devices.


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